Useful Linux Commands

Some useful Linux commands

• cat

  cat [file]

  • cat = dump file contents to terminal; ls -l to ensure small file

• df

  df -h

  • df = show disks space per partition
    • / = separate volume/disk for root os, logs
    • /data = separate volume/disk for websites, apps
  • -h = human readable size

• grep

  grep [search] [files]

  • grep = filter results, look for patterns in files
  • Example: grep Error *.log

• htop

  htop

  • htop = top list of processes, nicely colored; can sort, filter

• kill

  kill [pid]

  • kill = force stop/kill a process; only use for 'hung' process
  • [pid] = pid from ps aux list

• ls

  ls -lhtr [dir]

  • ls = list contents of directory
  • -l = details
  • -h = human readable sizes
  • -t = sort by time
  • -r = reverse sort, so new shows at bottom
  • -1 = just list names in a single column
  • Example: ls -lhtr logs/*

• ps

  ps aux

  • ps = process list
  • a = all, including other users
  • u = user format
  • x = register format
  • Example: ps aux | grep nginx

• reboot

  sudo reboot

  • reboot = reboot server; should not be needed; restart individual services

• systemctl

  sudo systemctl [action] [process]

  • systemctl = manage services such as nginx, php-fpm
  • Example: sudo systemctl status nginx
  • Example: sudo systemctl restart nginx
  • Example: sudo systemctl status php-fpm
  • Example: sudo systemctl restart php-fpm

• tail

  tail -f -n50 [file]

  • tail = returns the last few lines of a file
  • -n# = number of lines
  • -f = follow, useful for tailing an active log file
  • Example: tail -f logs/app.log

• vim

  vim [file]

• vim, vi = text editor; ls -l to ensure small file
• arrow keys = move cursor
• shift G = go to end of file
• ctrl u = page up
• ctrl d = page down
• /[patttern] = search for pattern
• esc = get out of most vi modes
• :q = quit
• :q! = quit without writing
• :wq = write, quite
• note, if quit a SSH session with a file vi-ed/open, be sure to SSH in again and cleanup the vi auto backup [file]~; vi-ing the original file again will prompt you about
• Example: sudo vim /var/log/messages

-End of Document- 

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